As NFL mandates Guardian caps in practice, area high school football teams have been using them for years, Sports
Why Alabama football players are wearing padded helmets in practice
What in the world are those weird-looking helmets the Saints are wearing in camp?, Rod Walker
NFL hopes to reduce head injuries with helmet experiment – The Morning Call
Cowboys wearing soft-shell helmets in practice as part of NFL mandate
Guardian Cap used by football teams to protect against head injury – The Denver Post
Guardian Caps: NFL requires use of helmet cover at training camps to reduce head injuries : r/nfl
What's with padded helmet caps teams are wearing
What are Glacier Peak players wearing on their helmets?